The present invention pertains to a method for fabricating an axially long cylindrical roll from shorter cylindrical wall sections and, more particularly, to a large diameter roll the outer cylindrical shell of which is provided with circumferentially spaced, axially extending steam and condensate bores.
Steam heated cylindrical rolls are well known in the art and are used in a wide variety of material treating applications. In one common application, webs of material to be treated are wrapped around the steam heated rotary roll which transfers heat to the web. Typically, steam is supplied to and condensate water removed from the interior of the roll via a non-rotating siphon system and connections to the roll shaft utilizing rotary joints for steam supply and condensate withdrawal. In order to optimize heat transfer from the steam to the outer surface of the drum, a preferable roll construction utilizes a plurality of axial passages formed in the interior of the cylindrical wall or shell of the roll. Steam is supplied to the axial passages at one end of the roll and condensate is removed from the passages at the opposite end of the roll.
In certain applications, such as in the paper industry, axially long and large diameter rolls are often used. These rolls may have a diameter of 72 inches (about 1830 mm) and an axial length of 400 inches (about 10 m). There is presently no known method for practically forming axial steam passages in a roll having an outer cylindrical shell of this length. One solution to this problem is shown in U.S. Pat. No. 3,217,795 where the cylindrical outer roll shell is formed by joining a number of axially shorter cylindrical wall sections, each of which is provided with cored or drilled axial bores which are aligned when the cylindrical roll sections are joined (as by welding) to form the final long cylindrical roll. However, a number of problems still remain in the fabrication of a roll of this kind. In a large diameter roll, there may be dozens or even hundreds of axial steam bores spaced circumferentially around the roll. It is very difficult to assure alignment of all of the bores from one cylindrical section to the next, even when the bores are formed with precision gun drilling methods. In addition, the desire to place the steam transfer bores as close to the outer cylindrical surface of the roll shell as possible has been compromised by the need to provide enough material thickness to accommodate an outer circumferential weld, joining the two cylindrical sections, of a depth sufficient to provide the necessary strength. In other words, the axial steam bores must be maintained radially inwardly from the outer surface of the shell a distance sufficient to preclude weld penetration into the bores when the roll sections are joined.